Method of fixing electrostatically produced images

ABSTRACT

AN ELECTROSTATICALLY PRODUCED, TONED IMAGE IS FIXED TO THE PHOTOCONDUCTIVE SURFACE BY CONTACT WITH FLUID AT ELEVATED TEMPERATURES.

United States Patent O No Drawing. Filed Jan. 18, 1971, Ser. No. 107,539 Int. Cl. C03g 13/20, 15/20 U.S. Cl. 117--21 1 Claim ABSTRACT OF THE DISCLOSURE An electrostatically produced, toned image is fixed to the photoconductive surface by contact with fluid at elevated temperatures.

BACKGROUND OF THE INVENTION This invention relates to the fixing of electrostatically produced images, and more particularly to the use of a heated liquid for fixing electrostatically produced images. The present invention is particularly adapted for use in producing lithographic printing masters although its use is not so limited.

In the process of forming an electrostatically produced image a photoconductive material is provided which is first completely charged and then exposed to light to dissipate the charge in the selected non-imaged areas to provide the desired latent image thereon. A particulate toner is then applied to the surface, which toner will adhere to the charged surface where a latent image has been formed. Such toner, when held on the surface only by the electrostatic charge is easily removed. Therefore, the toner is then fixed, either by pressure, or by heating to an elevated temperature. In fixing by heat the toner is heated to such a degree that it will firmly adhere to the surface on which it is disposed. This fixing by heat has conventionally been accomplished with high wattage ovens or by intensive heat lamps utilized to project radiant energy.

If the process is being utilized to form a printing master, the entire surface is then treated with a conversion solution, which chemically converts the non-imaged areas, i.e., the background photoconductive material, to water insoluble hydrophilic-oleophobic material. The fixed toner, in the form of the image, remains hydrophobicoleophilic. When ink is applied, the imaged areas of the master will receive ink, and print, while the background material will reject ink and not print. All of this is well known in the art.

One of the drawbacks to the above process is the need for high wattage heat producing lamps or ovens. Not only do these lamps or ovens require a large power input, they also present a potential fire hazard because of the heat generated. Also, very close control of the heat is required when it is applied in radiant energy form from lamps and ovens to prevent charring or damage to the support material.

SUMMARY OF THE INVENTION According to the present invention, electrostatically produced and toned images are fused by contact with a liquid maintained at a temperature sufficiently high enough to cause fixing of the particulate material, but low enough to prevent harmful degradation to either the support material or the particulate material being fixed.

3,706,588 Patented Dec. 19, I972 DESCRIPTION OF THE PREFERRED EMBODIMENT The process of the present invention, as described in the summary above, contemplates fixing an electrostatically produced image by contact with a liquid maintained at an elevated temperature.

To form an electrostatically produced image, a photoconductive material is provided on a support or backing member. This backing member can be either a sheet having the photoconductive material in a resin binder coated thereon, or it can be in the form of a continuous web, or in the form of a drum, or in any other form, wherein a film of photoconductive material is provided which can be charged and then selectively discharged to form the desired latent image. In the preferred embodiment, the support member is in the form of a lithographic printing master sheet having a backing paper with a photoconcluctive ZnO in a resin binder coated thereon. Particulate toner material in the form of a thermally responsive resin is then applied to the surface which toner will adhere to the charged areas, forming the desired image. This sheet, with the toner thereon, is then brought into Contact with a liquid, preferably by immersion therein, which liquid is maintained at a sufficiently high temperature to fix the particulate material, i.e., cause adherence of the particulate material to the support but not high enough to cause harmful degradation to either the support membet or the toner.

Toners conventionally are mixtures of natural and synthetic resins with suitable dyes and carbon black and are well known in the art. The exact temperature re quired to fix various toners varies and is determined by their composition. However, most toners of this type can be fixed at temperatures below 100 degrees centigrade. This is sometimes referred to as fusing the toner, although it is doubtful that complete or even any appreciable melting is required to obtain the necessary adhesion to the support. In the preferred embodiment the minimum temperature required to fix the toner is degrees centigrade. When heated to this temperature or above, the particulate material will adhere to the sheet, forming a copy with a relatively permanent image configuration thereon.

One very suitable liquid for fixing the image for lithographic printing masters is plain water. The water can be easily heated and maintained at temperatures of between approximately 80 degrees and the boiling point of approximately degrees centigrade. It has been found that immersion in hot water does not wash away the image, and that following the fixing by immersion, the master can be treated with a standard conversion solution and then utilized on conventional lithographic printing equipment.

The above description describes a process which is especially useful in producing lithographic printing masters. However, the process is not itself limited to producing masters but may also be used in other instances where it is necessary to fix the particulate material on the surface of a support member by application of heat.

Further, the exact method of applying the hot liquid may vary depending on many factors. For example, instead of immersing the support member in a confined body of liquid, the heated liquid could be sprayed on the support member as it is moved, or it could be applied by a fountain roll, or other methods. The important factor is that a sufiicient body of liquid be applied to transfer sufficient contained heat therein to perform the fixing function.

One of the outstanding advantages of the present invention is that there are no potential fire hazards involved, since a non-flammable liquid can be selected in most cases, and also since the temperatures involved are not extreme, as is the case in radiant energy fixing from ovens and high-wattage lamps. Further, the liquid is a convenient storage medium for the heat, as well as an excellent heat transfer medium to transfer the heat to accomplish the fixing of the image. The temperature of the liquid is easily regulated by means of conventional thermostats and heaters so that an exact temperature can be maintained. All of this contributes to lower power requirements for heat fixing.

What is claimed is:

1. In the process of making an electrostatically produced copy wherein thermo-responsive particulate material is arranged in a predetermined pattern on a photoconductive surface of a support member, the improvement comprising contacting the support member with a body of liquid sufiicient in size and heat content to effect a thermal fixing of said thermo-responsive particulate material without degrading said support member or said thermo-responsive particulate material, and maintaining said contact for a time sufficient to thermally fix said thermo-responsive material to said support member.

References Cited UNITED STATES PATENTS 3,567,484 3/1971 White et a1. 11721 3,318,698 5/1967 Schwertz 96-l.1 3,116,349 12/1963 Immel 264-46 3,515,855 11/1968 Mix 2l9'388 3,051,992 9/ 1962 Bradley 117l19.8 1,721,135 7/1929 Ross 117l19.8 2,125,827 8/1938 Turkington 1 17-1198 2,302,332 11/1942 Leekley 117l19.8

FOREIGN PATENTS 267,804 7/1964 Australia 355- -10 OTHER REFERENCES IBM Technical Disclosure Bulletin, vol. 12, No. 12, May 1970, p. 2117, Ralston et a1.

WILLIAM D. MARTIN, Primary Examiner M. SOFOCLEOUS, Assistant Examiner US. Cl. X.R. ll7-l7.5, 119.8 

